FIGS. 1 and 2 illustrate a first technique for taking account of regional variations in a statistical multiplexing system. More specifically, FIG. 1 illustrates the operation outside regional slots and FIG. 2 illustrates the operation during a regional slot.
The statistical multiplexing system comprises encoders (each associated with one of the television channels, a statistical allocator, switches and multiplexers.
Purely by way of an illustration, below in the description, we consider a plurality of television channels comprising six national channels (referenced N1 to N6) providing national programs and a group of four regional channels (referenced R1 to R4), each regional channel being associated with a different region (“region 1” to “region 4”) and providing regional programs during regional slots and sharing national programs outside of regional slots.
In this context and as illustrated in FIG. 1, the encoders associated with the national channels N1 to N6 are referenced EN1 to EN6, and those associated with the regional channels R1 to R4 are referenced ER1 to ER4. Each encoder receives programs from the television channel that is associated with it and generates an output signal. The output signals are referenced SN1 to SN6 for the encoders associated with the national channels N1 to N6, and SR1 to SR4 for the encoders associated with the regional channels R1 to R4.
The purpose of each encoder is to convert non-compressed television programs into compressed television programs in the context of encoding or to convert television programs already compressed according to the first encoding format into television programs compressed according to a second encoding format, in the case of transcoding. Here below, in the document, the two notions of encoding and transcoding will be regarded as being identical.
For each encoder working at a variable bit rate (VBR mode), the statistical allocator (reference AS) receives at least one piece of information coming from this encoder and provides a set of encoding parameters to this encoder. Thus, in the case of FIG. 1, the encoders EN1 to EN6 (associated with the national channels N1 to N6) and the encoder ER1 (associated with the regional channel R1) work at variable bit rate (VBR mode), and the statistical allocator receives information (referenced IN1 to IN6 and IR1 respectively) coming from these encoders and provides a set of encoding parameters to each of these encoders (the different sets of encoding parameters are referenced JN1 to JN6 and JR1). In the case of FIG. 2, the encoders ER1 to ER4 (associated with the regional channels R1 to R4) work at a constant bit rate (CBR mode) and only the encoders EN1 to EN6 (associated with the national channels N1 to N6) work at a variable bit rate (VBR mode). The statistical allocator receives the information IN1 to IN6 coming from these encoders and gives a set of encoding parameters JN1 to JN6 to each of these encoders.
The role of the statistical allocator is to dynamically select the set of encoding parameters of each encoder in order to optimize the video quality while at the same time complying with the bandwidth of the multiplexed signal (MPTS1 to MPTS4). In other words, each encoder communicates with the statistical allocator in order to send information (for example data on the state of the encoder and the complexity of the stream to be encoded) and receives new dynamic encoding parameters. For a given stream, each set of encoding parameters is defined not only as a function of the encoding criteria for encoding the concerned stream but also as a function of the criteria for the other streams managed by the statistical allocator. The statistical allocator can be present in different forms: it can especially take the form of an independent component or else it can be incorporated into already existing components of the system (encoder or multiplexer for example).
For each of the regions 2, 3 and 4, the system comprises a switch (referenced SWR2, SWR3 or SWR4), the output of which can be selectively either the output signal SR1 associated with the encoder ER1 associated with the regional channel R1 or the output signal SRi of the encoder ERi associated with the regional channel Ri with “i” equal to 2, 3 or 4 depending on the whether the region concerned is the region 2, 3 or 4.
For each region, associated with a given regional channel (among those referenced R1 to R4), one multiplexer (among those referenced M1 to M4) generates a multiplexed signal (among those referenced MPTS1 to MPTS4) resulting from the multiplexing of the output signals SN1 to SN6 of the encoders associated with the national channels and of the output signal SR1 of the encoder associated with a given regional channel, for the region R1, or of the output signal of the switch SWR2, SWR3 or SWR4, for each of the regions 2, 3 and 4. The multiplexed signals are for example multiple program transport streams (MPTS).
FIG. 1 illustrates the working of the system outside regional slots. In this case, the programs of the regional channels R1 to R4 are identical and correspond to a same national content (national program). The statistical allocator manages all the programs of the national channels N1 to N6 and the program of only one of the regional channels (R1 in this example), through the positioning of the switches SWR2, SWR3 and SWR4 in the “top” position). The programs of the national channels N1 to N6 and regional channels R1 to R4 are encoded in real time by the fleet of encoders. As already indicated above, the encoders EN1 to EN6 and ER1 work at a variable bit rate (VBR mode). The statistical allocator receives information IN1 to IN6 and IR1 coming from these encoders and gives them the sets of encoding parameters JN1 to JN6 and JR1 (one set per encoder). The bit rates computed by the statistical allocator are variable. Each multiplexer (one per region) generates a multiplexed signal containing the programs of all the national channels N1 to N6 (in the encoded form SN1 to SN6, at output of the encoders EN1 to EN6) and the program of the regional channel R1 (in the encoded form SR1, at output of the encoder ER1). The multiplexed signals MPTS1 to MPTS4 (one per region) are therefore identical (same cumulated bit rate and compliance with the constraints of statistical multiplexing).
FIG. 2 illustrates the operation of the system during a regional slot. During a regional slot, the programs of the regional channels R1 to R4 are not identical. Each regional channel which does a regional variation can transmit a regional content (regional program) proper to it. When a regional variation is reported (for example by an SCTE-35 type trigger or SCTE 104 type trigger or any unspecified external trigger), a dynamic reconfiguration of certain key components of the system is done. Thus, the encoders ER1 to ER4 (associated with the regional channels R1 to R4) work at a constant bit rate (CBR mode). Only the encoders EN1 to EN6 (associated with the national channels N1 to N6) work at a variable bit rate (VBR mode). The statistical allocator therefore receives only the information IN1 to IN6 coming from the encoders EN1 to EN6 and provides a set of encoding parameters JN1 to JN6 only to each of these encoders. Besides, the switches SWR2, SWR3 and SWR4 pass into the “low” position enabling each of the multiplexers M1 to M4 to multiplex, with the programs of all the national channels N1 to N6 (in encoded form SN1 to SN6, at output of the encoders EN1 to EN6), the program of one of the regional channels R1 to R4 (in encoded form SR1 to SR4, at output of one of the encoders ER1 to ER4). In other words, the multiplexer M1 receives the signals SN1 to SN6 and SR1, the multiplexer M2 receives the signals SN1 to SN6 and SR2, the multiplexer M3 receives the signals SN1 to SN6 and SR3, and the multiplexer M4 receives the signal SN1 to SN6 and SR4. The multiplexed signals MPTS1 to MPTS4 (one per region) are therefore different.
The first known technique has several drawbacks during a regional variation:                the regional variation must be simultaneous in all the regions. This implies a very precise triggering so that the regional variation is as transparent as possible from the viewpoint of the user's experience. In addition, this makes it impossible to manage scenarios of the type entailing the local insertion of programs or advertisements without carrying out a global variation throughout all the regions;        operational complexity: the regional variation requires the dynamic reconfiguration of the key components of the system (namely the encoding fleet, the statistical allocator, the switches and the multiplexers), and this must be done simultaneously;        the efficiency of the statistical allocator is impacted, this being due to the reduction of the bandwidth, part of which is allocated to the regional channels, the programs of which are encoded at constant bit rate (CBR mode). This constraint is necessary in order to ensure a constant totalized bit rate in each region.        
FIG. 3 illustrates a second known technique for taking account of regional variations in a statistical multiplexing system. As compared with the first known technique, there is duplication for each of the regions of a fleet of encoders (comprising the encoders associated with the national channels and one encoder associated with the regional channel of this region) and a statistical allocator. This enables the use of a variable bit rate (VBR mode) for all the canals, (i.e. for all the television channels, whether national or regional).
More specifically, for a region i with iε{1 . . . 4} in the example illustrated, the system comprises the encoders EN1 to EN6 and ERi, the statistical allocator AS (which receives the pieces of information IN1 to IN6 and IRi coming from these encoders and gives them the sets of encoding parameters JN1 to JN6 and JRi) and the multiplexer Mi (which generates the signal MPTSi by multiplexing the signals SN1 to SN6 and SRi coming from these encoders).
The major drawback of the second known technique is the exponential cost in terms of infrastructure since the operator must duplicate the encoders and the statistical allocator as many times as there are existing regions (one network head-end per region).